This protocol describes a longitudinal research project which will examine changes in on-road driving performance and changes in {cognition} among actively driving subjects with Alzheimer's disease. It is well recognized that dementia is a risk factor among the elderly for motor vehicle crashes and fatalities. Degenerative dementias such as Alzheimer's disease, because of their progressive nature, eventually lead to driving incompetence in all cases. A critical question that faces clinicians in everyday practice is when to advise patients with early disease to abstain from driving. Because patients with Alzheimer's disease may still be competent to drive if their dementia is in its earliest and mildest stage, and because driving is an important factor in maintaining autonomy for elders, licenses should not be revoked based on arbitrary decisions about one's memory ability. Annual road testing for driving competence of all elders or even all elders with dementia is neither practical nor economical. Therefore, an effective screening instrument is badly needed. Knowledge about the actual driving impairments that occur in dementia patients that lead to hazardous driving and how they relate to changes in neuropsychological function over time is critical to the development of a valid screening tool. Drivers with early stage Alzheimer's disease will be enrolled in this study and followed every six months over {two to} three years. A recently validated road test protocol will be administered by a professional driving instructor. {Computerized} neuropsychological tests of visual perception, visual attention, and executive function will be administered concurrently. It is predicted that the earliest evidence of driving impairment will be associated with disturbances {in visual perception and attention.} In more advanced stages of dementia, when subjects are most likely to be judged as incompetent drivers, there will be prominent deficits in executive function as well. The longitudinal design of this study will give important insights into the evolution of driving impairment among AD patients and assist in the future development of screening tests to identify hazardous drivers who would be likely to fail a performance based road test.